Cinchonism

Cinchonism or quinism is a pathological condition caused by an overdose of quinidine or its natural source, cinchona bark. Quinine is medically used to treat malaria. In much smaller amounts, quinine is an ingredient of tonic drinks, acting as a bittering agent. Cinchonism can occur from therapeutic doses of quinine, either from one or several large doses. Quinidine (Class 1A anti-arrhythmic) can also cause cinchonism symptoms to develop with as little as a single dose.

Most symptoms of cinchonism (except in severe cases) are reversible and disappear once quinine is withdrawn.

Quinine, like chloroquine, inactivates enzymes in the lysosomes of cells, and has an anti-inflammatory effect, hence its use in rheumatoid arthritis. However switching off these enzymes can also cause abnormal accumulation of glycogen and phospholipids in lysosomes, causing a toxic myopathy. It is possible this is the root cause of cinchonism.